Development of a 2 MW+ High Power Density Induction Motor for Electric Aircraft Propulsion Using Cryogenic Aluminum Windings

Our team has developed and de-risked a design for a 2.1 MW high power density motor intended for electric aircraft propulsion as part of an ARPA-E program. The power density achieved for the motor+drive in this design was 17.5 kW/kg with 96.8% efficiency for the motor+drive in cruise. The motor is an asynchronous design with an outrunner rotor configuration, based on previous developments at OSU CAR. However, the stator and rotor windings are cryogenically cooled monolithic aluminum conductors. The Al is three-nines, and the target operational temperature is between 60-120 K. Originally conceived as using LNG as the cooling media, we broadened the design to allow for a secondary cooling loop with a variety of primary fuel coolants, including LNG and liquid hydrogen. The work gives an overview of the development of the overall design and design philosophy, magnetic circuit, and thermal design of the motor, with references to our previously published work on this program related to cryogenic power electronics and de-risking studies for the cooling circuit. Flow cooling studies are described along with basic magnetic circuit, coolant flow design, and structural design. Our approach starts with the rotating machine requirements and the cryogenics are adapted as needed for a novel solution; this leads to a solution with a cool annular region, with a warmer region near the rotational axis and near the motor periphery. The solution we found is a highly viable one, with very high performance.